Because of their excellent mechanical properties, particularly high modulus and strength, and high resistance to light and water, polyesters, a typical example of which is polyethylene terephthalate, are widely used as a material for the production of fibers, films and other shaped articles. On the other hand, because of their excellent abrasion resistance, dyeing property and chemical resistance as well as excellent mechanical strength, polyamides, a typical example of which is polycaprolactam and polyhexamethylene adipamide, are widely used as a material for the production of fibers, films and other shaped articles which are used for purposes other than those of the polyester products.
Polyesters and polyamides have their individual excellent properties as described above. However, two types of these polymers also have disadvantages. In order to eliminate their respective disadvantages, it was attempted, heretofore, to combine these polymers with each other. For example, in order to impart an excellent dyeing property and a high abrasion resistance to the polyester, it was attempted to combine a polyester component with a polyamide component as a modifier. Inversely, in order to improve a low rigidity of the polyamide and a change in the physical properties due to its hygroscopicity, it was attempted to combine a polyamide component with a polyester component as a modifier. However, as far as the inventors of the present invention know, most of the conventional attempts have not succeeded in putting a polyester amide having an ester linkage and an amide linkage in the molecule to practical use. Only in the field of heat-resistant resins, a process for producing a polyester amide from a dicarboxylic acid containing an amide linkage and a diol is known. However, this is a very special case. This process requires the use of expensive starting materials and thus, is not suitable for general use. Also, the process steps and the performance of the polyester amide are extremely unique.
As an example for general examination, there can be mentioned a process for producing a polyester amide which comprises melt-mixing a polyester such as polyethylene terephthalate and a polyamide such as polycaproamide to effect a partial ester-amide exchange reaction, thereby producing a polyester-polyamide block copolymer. This process has the disadvantages that because of poor compatibility between the polyester and the polyamide, only a very small amount of the co-component can be introduced into the base component, and the mixture tends to decompose, which results in a colored product.
In another attempt, the introduction of the co-component was carried out at the polymerization stage. However, in the case where an ester-forming compound is present in a polyamide polymerization system, a high polymer can not be obtained due to the hydrolysis of the resulting ester component. On the other hand, in the case where a polyamide-forming component is present in a polyester polymerization system, for example, when the polyamide-forming component is .epsilon.-caprolactam, the lactam is distilled off from the polymerization system, and when the polyamide-forming component is a hexamethylenediamine-adipic acid salt, this compound is incompatible with the polyester-forming component and exhibits a poor reactivity thereto. Therefore, a useful polyester amide can not be obtained.
The inventors of the present invention found that when a specific polyamide-forming component and a specific polyester-forming component are copolymerized with each other, a polyester amide copolymer having a high degree of polymerization and exhibiting performances which could not be anticipated in the past can be obtained without encountering the above-mentioned problems in the production process, such as poor compatibility, low reactivity, coloration and monomer vaporization.
It was found that the specific polyester-forming component and the specific polyamide-forming component undergo uniform polymerization without causing phase separation over a total range of copolymerization composition, thereby providing a non-colored polymer having a high degree of polymerization, and that the resultant polyester amide is a flexible polymer excellent in mechanical strength, impact resistance, transparency, softness and solvent solubility, and therefore, it is useful as a material for the production of fibers, films and other shaped articles.
The polyester amide having a specific composition has a high adhesive strength to general fibers and provides an adhesive joint having an excellent hand and exhibiting a high water resistance and a high resistance to perchloroethylene (high dry-cleaning resistance). Therefore, this type of polyester amide was found to be a useful material as a hot-melt adhesive for fibers.
In addition, the polyester amide having another specific composition has a high adhesive strength to metallic materials such as copper, aluminum, tin, iron, stainless, tinplate and chromium-treated steel plate and provides an adhesive joint excellent in processability and stability. Therefore, this type of polyester amide was found to be a useful material as an adhesive for metals.
In addition, the polyester amide of the present invention exhibits a unique heat-sensitive property and thus, it was found to be a useful heat-sensitive material.
On the basis of the above mentioned backgrounds, the present invention was accomplished.